<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <form action="">

        <!-- autofocus 自动焦点 
        required 必填项 不能为空   
        multiple 可以填写多个邮箱地址 逗号隔开
        pattern 正则表达式

        -->
        <div>
            用户名：<input type="text" name="" id="" autofocus required pattern="[a-z][1-9]{3}">
        </div>
    
        <div>
            邮箱：<input type="email" name="email" id="" required  multiple>
        </div>

        <input type="submit" name="" id="">
    </form>

    

</body>
</html>